Open Data supplied by Natural Environment Research Council (NERC)

Falmouth Scientific Inc. OEM CT sensor

The OEM CT sensor is designed to provide high accuracy conductivity and temperature measurements in a package that can be readily integrated into user systems. The CT sensor relies on an inductively coupled conductivity sensor, with a large inside diameter that eliminates the need for pumps. A high grade Platinum Resistance Thermometer is used to measure temperature.

Sensor specifications are given in the table below. Since 2009 this instrument has been manufactured by Teledyne RD Instruments as a Citadel CT-EK Sensor. More information about the instrument can be found on the Teledyne Citadel specification sheet .

Sensor Specifications

Instrument Parameter

Small CT Cell Conductivity

Large CT Cell Conductivity

Temperature

Range

0 to 70 mS cm -1

0 to 70 mS cm -1

-2 to 35 degrees C

Accuracy

±0.020 mS cm -1

±0.010 mS cm -1

±0.050 degrees C

Stability

±0.005 mS cm -1 mo -1

±0.003 mS cm -1

±0.005 degrees C mo -1

Response

20 cm @ 1 m s -1

15 cm @ 1 m s -1

20 seconds internal, 1 second external

Power Input

50 mW @ 6 VDC, voltage range 6 - 14 VDC

Logic

2 0 - 5 VDC control lines

Output Impedance

500 ohms

Cefas SmartBuoy data processing

This document outlines the procedures in place at Cefas in August 2005 for processing and quality assuring SmartBuoy data.

Raw data files are processed and the data move through 4 levels, starting with raw data at level 0 through to level 3, where data are fully quality-assured and expressed in appropriate units. The application of the procedures at each level result in data deemed fit to progress to the next level.

Cefas Quality Assurance (QA) Protocols

At Level 0, raw binary data files from the loggers are transferred to the network.

Automated checks - Level 1

Level 1 involves applying automated quality assurance procedures to the data. These include the following steps:

Burst data are loaded into memory for processing.

Calibration data for all instruments and sensors used on the deployment are retrieved from the SmartBuoy database. These may be manufacturers' sensor calibrations or the most current laboratory calibrations. Instruments are returned to the manufacturer and re-calibrated at regular intervals.

Burst data maximum and minimum ranges are checked and flagged if they fail the checks.

Burst means, result count, and result standard deviation are calculated from non-flagged burst data.

If there are data from two PAR sensors at different depths, Kd (m -1 ) is calculated for burst mean data only as LN(PAR1m/PAR2m).

Burst mean data maximum, minimum and rate of change checks are carried out and flags applied to any failures.

Time stamped burst and burst mean data with default units are stored on SmartBuoy database.

The data are now at QA status = 1.

Manual checks - Level 2

Level 1 burst mean data are now ready for manual QA procedures in order to progress to Level 2. Deployment notes are consulted for any comments on sensor performance or malfunction and post-deployment photographs of sensors, if available, are examined.

Cefas use a data visualisation tool to examine the SmartBuoy data.

A comparison is made between the end of one deployment with beginning of the next to identify possible drift and/or biofouling of OBS, Fluorometer, Salinity, PAR, and oxygen sensors.

Battery voltages are checked for sudden jumps and, if present, other sensors are examined for similar jumps to determine whether there is a problem with the sensor or if the buoy was disturbed.

Reference voltages on the FSI CT module are checked.

The standard deviation of OBS is examined. A steady increase in standard deviation is a good indication of the onset of biofouling. It is also used as a rough indicator for fluorometers during summer, except during spring, when there are large fluctuations in chlorophyll.

Li-Cor is examined for fouling, which could be indicated by a steady drop in daily maximum or a steady increase in standard deviation. If above-water Li-Cor data are available, they are used for comparison.

Pressure is examined for sudden decreases, indicating when the buoy was taken out of the water.

Roll and pitch are examined for any anomalies. It is expected that the spring/neap cycle will be present in the buoy tilt signal.

Where possible, comparison is made between burst mean data from sensors measuring the same variable. This is in order to determine whether there is a systematic offset (drift) or sensor fault and whether biofouling is present.

Comparison is made between burst mean sensor outputs from different variables as this can be helpful in determining the onset of biofouling. Any data that fail the checks are flagged with flags specific to the check that was failed.

Calibrations - Level 3

The combined information from Level 2 is used to determine the periods during which the data series are considered suspect. The data have now reached QA status = 2 and can progress to Level 3, where they will be fully calibrated with field-derived sample data.

For salinity an offset is calculated as the difference between result output from logger and the result from a discrete sample collected at the same time.

Calibration from regression analysis of field samples and logger output is applied to derive new parameters, e.g. chlorophyll calculated from fluorescence, suspended load calculated from OBS.

Chlorophyll calibrations are determined from GF/F filtered water samples, which are extracted in acetone and measured for fluorescence using a Turner Designs Fluorometer.

Suspended matter calibrations are determined from a known volume of water sample filtered through pre-weighed 0.4 µm Cyclopore filters. The filters are dried and reweighed to determine the weight of material per unit volume.

Salinity is calibrated using water samples that have been analysed with a Guildline Autosal salinometer.

Water samples from the Aqua Monitor are analysed for nutrients by colorimetric analysis of 0.4 µm Cyclopore-filtered samples.

The data have now reached QA status = 3 as time stamped, field calibrated burst mean data with parameter codes and units stored on SmartBuoy database with associated uncertainty or 95% confidence limits as appropriate. All SmartBuoy data banked at BODC have passed full Cefas QA procedures. Data that fail the Cefas QA checks are not submitted for banking.

SmartBuoy data processing by BODC

The following outlines the procedures that take place at BODC for banking Cefas SmartBuoy data.

BODC receives SmartBuoy data from Cefas after all quality checks have been passed and all possible calibrations applied. The data files are submitted as separate MS Excel spreadsheets for each parameter, i.e. there are separate files for temperature and salinity from the same instrument. An exact copy of the data is archived for safekeeping upon arrival.

Once the submitted data files are safely archived, the data undergo standard reformatting and banking procedures:

The data files are reformatted using an in-house program into a common format, which is a NetCDF subset.

Data files arising from the same instrument are combined into a single file.

Standard parameter codes are assigned that accurately describe the data.

Unit conversions are applied, if necessary, so that units are standardised. Oxygen concentration supplied by the originator in units of mg l -1 is converted to µmol l -1 by multiplying by 31.25.

The data are screened visually and any spikes or instrument malfunctions can be clearly labelled with quality control flags.

Comprehensive documentation is prepared describing the collection, processing and quality of each data series.

Detailed metadata and documents are loaded to the database and linked to each series so that the information is readily available to future users.

Proudman Oceanographic Laboratory Coastal Observatory

The Coastal Observatory was established by Proudman Oceanographic Laboratory as a coastal zone real time observing and monitoring system. The main objective is to understand a coastal sea's response both to natural forcing and to the consequences of human activity. Near real-time measurements will be integrated with coupled models into a pre-operational coastal prediction system whose results will be displayed on the World Wide Web.

The Observatory is expected to grow and evolve as resources and technology allow, all the while building up long time series. A site selection pilot study was carried out in September 2001 and the Observatory became operational in August 2002.

The site is located in Liverpool Bay and is subject to typical coastal sea processes, with strong tides, occasional large storm surges and waves, freshwater input, stable and unstable stratification, high suspended sediment concentration and biogeochemical interaction. Measurements and monitoring will focus on the impacts of storms, variations in river discharge (especially the Mersey), seasonality and blooms in Liverpool Bay.

A variety of methods will be used to obtain measurements, including:

Moored instruments for in situ time series of currents, temperature and salinity profiles, and surface waves and meteorology. It is hoped that turbidity and chlorophyll measurements will be made at another site as the Observatory progresses;

The Cefas Smartbuoy for surface properties such as nutrients and chlorophyll, starting late 2002;

R.V. Prince Madog to carry out spatial surveys and service moorings;

Instrumented ferries for near surface temperature, salinity, turbidity, chlorophyll and nutrients. The first route will be Liverpool to Douglas, Isle of Man, starting late 2002;

Drifters for surface currents and properties such as temperature and salinity, starting in 2004;

Tide gauges, with sensors for meteorology, waves, temperature and salinity, where appropriate;

Smartbuoy deployment LB2_012

Deployment and Recovery

This rig was deployed as part of the Liverpool Bay Coastal Observatory during R.V. Prince Madog cruise PD29_06. The weather was stormy throughout the cruise (force 6 - 9), however, since the winds were from the south and southeast all of the moorings work was successfully achieved. Recovery of the rig took place during R.V. Prince Madog cruise PD35_06, there were variable winds of force 3 with slight swells.

Rig Position

53 26.908N, 3 38.823W

Water Depth

27.3m

Deployed

22 September 2006 09:34

Recovered

02 November 2006 12:57

No. of days

41

Rig Description

This rig is a single line mooring, comprising a surface CEFAS SmartBuoy. The single point mooring was mainly composed of 0.5 inch long link chain and marked at the surface by a 1.8 m diameter toroid (the CEFAS SmartBuoy) and anchored by a half tonne clump of scrap chain. The CEFAS Smartbuoy contains a suite of instruments mounted just below the surface.

Fixed Station Information

Station Name

Coastal Observatory Site 21

Category

Offshore location

Latitude

53° 27.13' N

Longitude

3° 38.48' W

Water depth below MSL

25.0 m

Liverpool Bay Coastal Observatory Site 21

This station is one of 34 stations regularly visited by the Proudman Oceanographic Laboratory (POL) as part of the Liverpool Bay Coastal Observatory. The main activity at this site are CTD profiles (since August 2002) which are taken during each site visit. This station was also the secondary mooring site (also referred to as Site B) for the Coastal Observatory project between April 2005 and March 2010. After March 2010 the moorings were moved to site 20. The station lies within a box of mean water depth 24 m with the following co-ordinates:

Box Corner

Latitude (+ve North)

Longitude (+ve East)

North-west corner

53.46028

-3.658

South-east corner

53.44249

-3.6105

The position of this station relative to the other POL Coastal Observatory sites can be seen from the figure below.